Both are using encryption. They have a bit of a bad reputation, since Excel and WinZip used to use dreadful encryption methods in the past. However, the latest versions of both use AES-128, which the US Government considers strong enough to use for SECRET information. You don't tell us your threat model (what you are protecting and who from) so we can't make any guarantees, but you should be OK with whichever is the most convenient.

However, two important points to note:

I am talking here about Excel's "password to open" option where you can't open the worksheet at all. The "password to modify" option does not encrypt and is trivial to bypass.

Information Security is more than just picking a strong encryption method. You also need to use strong passwords, manage the password exchange process, secure the endpoints, guard against social engineering, etc. etc. etc.